Copper has to be plated with a tarnish resistant metal to be used in any kind of contact scenario. Typically nickel is used but gold alloys and rhodium are better performing plating materials, albeit a lot more expensive.
Spring steel can be an issue for battery contacts in that steel itself is not a particularly good conductor. It has to have a heavy plate with a good conductor, usually a copper base plate followed by nickel or something better. For low power applications cheaply plated spring steel contacts are not as much of an issue, but with the high currents that can be encountered powering an atomizer, these issues become much more significant. This is why people often have problems with the cheap battery holders you find on eBay or from electronics shops.